


TwixtTale: Their Story

by SoloShikigami



Category: Undertale (Video Game)
Genre: Alternate Universe, F/F, Gen, Gender or Sex Swap, Genocide, Multi, Needles, Pseudo-Incest
Language: English
Status: In-Progress
Published: 2017-03-25
Updated: 2017-04-27
Packaged: 2018-10-10 08:58:05
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,225
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10434099
Author URL: https://archiveofourown.org/users/SoloShikigami/pseuds/SoloShikigami
Summary: Frisk was always curious about Sans and Papyrus' backstory, so one day they decided to ask. Sans was a story-teller, after all, and if they didn't get the whole truth they would at least be entertained. But Sans has no desire to spin any fiction into this, so Frisk will get the story that they asked for.Whether they like it or not.





	1. Let's start at the very beginning.....

**Author's Note:**

> Hello all and welcome to the AU TwixtTale! Please mind the tags and the notes as this story goes along, there will be incest/fontcest at least implied, but I'm not sure how far it will go, so if that's not your thing then this probably won't be your story.
> 
> If it's all good, please proceed and have fun!

            Frisk and Sans sat at the far right side of the bar, their usual spot when they went to Grillby's, and waited for their order. Frisk swung their feet, brushing some lint from their skirt. Sans tapped her fingers on the bar, leaning against her hand, her eyes sleepy, her face relaxed - Frisk had a hard time remembering the last time she didn't have an underlying look of wariness about her.

            "Thanks, B," Sans murmured as the fire elemental slid a bottle of Sans' favorite condiment down to her.

            "Fresh batch," Grillby said with a small wink, turning quick enough to make her little black skirt flounce as she walked back to the kitchen.

            Sans grinned. "That woman spoils me," she squeezed the bottle of honey mustard sauce into her mouth. “If I didn’t know any better, I’d think she was flirting.”

            "You know," Frisk murmured. "I just realized that there is a lot about you and Papyrus that I don't know."

            Sans chuckled. "You've had what, three years to figure that out?"

            Frisk crossed their arms on the bar and rested their head, still looking at Sans. “You know, there’s really nothing else we have to do today; we already picked up snails for Asgore, you made sure that one sock Papyrus keeps telling you to pick up is still sitting in the living room, and Papyrus is running the rest of the errands,” Frisk picked their head up and propped up a hand to rest it on with a grin. “Come on, you’re the story-teller. Tell me a story.”

            “Heh, I’d think with a full name like Comic Sans, I’d be a comedian,” she mused. “But, no, gifted with some simple story-telling abilities. You gotta be careful what you wish for though, kid, you may just get it.”

            “Yeah?”

            “Yeah. And you may not like it.”

            Sans took another sip of the honey mustard, swallowing it slowly, feeling the bits of mustard seed scraping her throat. She waited a moment as a yellow-orange flame caught her eye and Grillby set their plates of hamburger and fries in front of them and she reached under the bar for another bottle of honey mustard for Sans and slid a bottle of ketchup to Frisk. Sans tipped her bottle in thanks and Grillby winked before skipping back off.

            “Definitely flirting,” Sans murmured.

            “Why would you say I wouldn’t like it?” Frisk asked, checking that the cap of the ketchup bottle was properly on before attempting to squeeze any out.

            “Hell, kid, I don’t like the story much myself.”

            “If it’s really that bad, Sans,” Frisk said, looking worried and putting a hand on her arm. “You don’t have to tell me.”

            Sans grunted a little, drinking the rest of the bottle with a sigh and nearly tossing the bottle aside, one hand reaching up to touch the ever-present band of lace wrapped around her head. Frisk tilted their head, realizing just then that this was the first time they had really looked at it up close.

            “Nah, you deserve to know. After everything we’ve been through, you deserve the story.”

            “For what it’s worth, thank you,” Frisk said. “So where do we start?”

            Sans gave a slight shrug, poking at a fry. “The same place most stories start; the beginning.”

 

~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~

 

            _“My first memories are vague ones, as I’m sure most everyone’s are. I think I was five years old or so, but I’m going to go back even before that. It’s what I know from what I’ve been told, and I guess we’ll just go from there.”_

 

            It had been a while since the monsters were banished underground. They had tried to begin establishing a kingdom from where they first arrived, however the structures fell into ruins as they moved on and found other places they preferred to live. The king had decided that it was likely for the best, as trying to squeeze everyone into such a small area was proving to be tricky.

            After some more time had passed, settlements established themselves and the king and queen built the capital and their palace. While they were, of course, not part of the surface world, some of its influences still made it to the Underground. Pieces of technology started to come down to them in piles of what looked to be garbage; books and tapes and DVDs began to show up in odd places in Waterfall.

            Monsters were an intelligent, capable species and were quick to pick up on the technology, and mixing it with their magic.

            This meant that all in all, it didn’t take long for monsters to start looking for a way to regain their freedom.

            “Your Highness, may I present to you Dr. Gaster,” a guard announced.

            King Toriel stood with a smile and open arms. “Welcome, Dr. Gaster! I am so pleased and honored to have you here.”

            “The honor is mine, your highness,” Dr. Gaster said with a bow.

            “Come and walk with me.”

            Dr. Gaster followed the king, her hands folded behind her back.

            “I understand that your field of research tends to be physics and psychology,” King Toriel said.

            “Yes, sir,” Dr. Gaster confirmed.

            “Have you ever done research on souls?”

            “Souls, sire?”

            “Yes.”

            “Well, no, I have not, and I can’t say that I ever met one who did.”

            King Toriel nodded and brought Dr. Gaster into a hallway that seemed to go far away from the main part of the castle.

            “As king, it is my duty to uphold the hopes and dreams of my people, Dr. Gaster. This I’m sure you are well aware of. I want us to be free again, it has been too long and I am afraid that while I have tried to make living down here tolerable for all monsters, I know many of my subjects are unhappy.”

            “I must admit, your grace, it has been a concern of mine.”

            Dr. Gaster took one hand on place it gently on her middle. King Toriel noticed the motion and smiled.

            “You and Aggy have quite a bit in common, I see.”

            Dr. Gaster smile widened in return. “How may I be of assistance?”

            They had reached the end of the long hallway and reached a door that looked heavy and was heavily guarded. Not only were there two actual guards dressed head to toe in heavy black armor, bouncing and waving their swords in sync, as if itching for battle, but multi-colored tiles lit up the floor beyond them.

            “Your Highness,” one guard said.

            Both guards stopped moving and they kneeled on the ground, lowering their weapons. The second reached over and pressed a button near the wall. The tiles all changed to pink.

            “The pink tiles do nothing,” King Toriel said. “Come along.”

            They moved through to the doors and went inside. Dr. Gaster soon found herself gasping in shock at the odd landscape that stretched before her. It seemed to go on forever, light and dark mixing in an odd dance to music that she couldn’t hear.

            “That, my dear, is the barrier,” King Toriel said solemnly. “I want to know how to bring it down for good so we can be free again. I understand you are one of the top people in your field, if not the absolute top. I will make sure you and your family are well taken care of, you’ll want for nothing, if you will study this for me and find a solution.”

            Dr. Gaster continued to stare, mesmerized by the odd field of magic before her, and let King Toriel’s words wash over her at first, then they slowly sank in and she nodded in understanding.

            “I appreciate the opportunity,” she said with a smile, turning to her king. “When shall I begin?”


	2. Establishment

**Summary for the Chapter:**

> Dr. Gaster and Sans’ life in the beginning, when Sans was just a baby bones.

            “Sans! You get back here this instant!”

            “Nyah, nyah, can’t catch me!” the tiny skeleton monster giggled as she rounded a corner.

            “You are in such huge trouble, young lady!”

            Sans just giggled, darting into the next room and hiding behind a huge armchair. She tried to be as quiet as she could, peeking around the brown fabric and glancing around with anticipation.

            Suddenly, Sans shrieked when her feet left the ground and bony fingers squeezed her sides, tickling her.

            “I got you!” a voice said in a sing-song.

            “Mommy! Stooooop!” Sans whined through a giggle as her mother cradled her.

            “Then stooooop running away from me!”

            They both laughed as she dropped into the chair and Sans moved to sit on her lap, facing her.

            “How are you doing today, Sans?” her mother asked, smiling as she caressed the side of her skull.

            “Good, Mommy!”

            The mother tilted her head, her eyes betraying her disbelief. “I’m glad that you’re feeling all right, but we still have to test you and see what’s going on.”

            Sans frowned and crossed her arms. “Don’t wanna.”

            “I know, baby bones, I know,” she murmured, pulling her daughter close to her chest.

            Sans snuggled into the warm embrace with a sigh, her exhaustion apparent as the strain of the short chase nearly drained what little stamina the baby skeleton had.

            Dr. Gaster frowned, running a _check_ on her daughter and sighed at the stats that were lower than what they should have beem.

            “You know, you’re the best thing that’s ever happened to me?” Dr. Gaster murmured against her baby’s skull.

            “You the best, too,” Sans murmured, looking up with tired eyes.

            Mother and daughter shared a smile before dozing off in the warm afternoon.

 

\- ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ - ^ -

 

            “Miss- oh, I’m sorry, Dr. Gaster?”

            Sans immediately hid under the children’s table, bumping it and causing the other toddlers to make various noises of protest. Her mother sighed, apologizing to the other parents as she fished her daughter out from under the table.

            “Please, Sans, I know you don’t want to be here. I don’t want to be here, either,” she murmured as the child gripped arms and legs around her mother as tight as she could.

            Sans was the type to refuse to cry, but she couldn’t stop the tears and buried her head into her mother’s shoulder. She chanced a peak up after a while; it was usually about then that they asked her to step on the scale, stand up straight to be measured, and attach the weird cuff on her arm to monitor her magic level, but none of that seemed to happen. She saw that the nurse was leading them into a room where her doctor, Dr. Helvetica, was seated behind a desk.

            Dr. Helvetica was also a skeleton monster, like Sans and Dr. Gaster.

            “Good to see you, Dr. Gaster. Hello, Sans!” Dr. Helvetica said, giving the baby a finger wave.

            Sans gave him a small grin, still clinging to her mother. She did like her doctor, despite all of her apprehension.

            “You can just call me Aster,” Dr. Gaster said with a smile and nodded in appreciation as Dr. Helvetica invited her to sit.

            “Thank you, Aster. Here you are, Sans, I took the liberty of having your favorite friend waiting here for you,” Dr. Helvetica said, handing over a stuffed skeleton dolly.

            Sans glanced from the dolly to Dr. Helvetica warily, looking up at her mother with unsure eyes.

            “It’s all right, darling,” she said soothingly. “Be sure to say ‘thank you.’”

            “Thank you,” Sans mumbled, reaching for the dolly but not far enough to actually take it.

            Dr. Helvetica chuckled and leaned forward to press it into Sans’ hand, who gripped it then sank back into her mother’s embrace to cuddle the toy.

            “Still a little wary and distrusting, I see,” Dr. Helvetica said almost sadly.

            “Some toddlers are, are they not?” Dr. Gaster said, stroking her little one’s skull.

            Dr. Helvetica smiled, nodded, then sat back in his chair with a small sigh, bringing his fingertips together in front of his mouth and giving Dr. Gaster a serious look.

            “ _~I’m sorry to say that I have some bad news,~_ ” Dr. Helvetica said, speaking in the language knows as ‘hands.’

            Dr. Gaster stiffened. “ _~What is it?~_ ”

            “ _~I’m afraid that Sans has the same illness many skeleton monsters are coming down with – osteoaborisci. As you know, our numbers are dwindling and it is due to this disease.~_ ”

            It had been a tragedy happening over the past decade or so; a degenerative illness that only affected skeleton monsters was slowly but surely killing them off. There was no particular rhyme or reason, and though scientists and doctors were scrambling for answers there simply weren’t any.

            Dr. Gaster took a deep breath, trying to not show any signs of distress, especially with her precious one in her lap.

            “ _~Aster, I am terribly, terribly sorry.~_ ”

            “ _~What do I do, Dr. Helvetica?~_ ” she asked. “ _~What’s going to happen to my baby?~_ ”

            “ _~I wish I knew. There are medications to slow the process, though I must tell you that your child is the youngest one who has contracted the disease; most of the time we find it in older adolescents or adults.~_ ”

            “ _~What significance does that hold?~_ ”

            “ _~A few possible theories, such as now we wonder if the disease could be partially genetic; was she born with the proper makeup and did something trigger the disease to show up? It is a mere theory that I’ve come up with, but since we do have a doctor-patient confidentiality, I have not voiced my theories or findings to anyone,~_ ” Dr. Helvetica leaned forward, putting his elbows on his desk. “ _~Aster, this is heavy news, and I know it can’t possibly be easy to hear. I don’t want you to do anything rash or out of desperation. Right now, I think you should start Sans on the lowest possible dose of inhibitor medications to slow the disease down. You have perhaps eight months to a year before real trouble could start without it.~_ ”

            Dr. Gaster nodded slowly as she let the words sink in. She felt hot tears pricking the edges of her eye-sockets.

            “ _~I hope you don’t take this the wrong way, but I want a second opinion,~_ ” Dr. Gaster said evenly.

            Dr. Helvetica nodded. “ _~I expected as much. I encourage you to explore this and I hope I am wrong. I am still going to prescribe you the inhibitor, and I do suggest that you start her on it as soon as possible. I prepared a list of a few other doctors and pediatricians, some are specialists in rare diseases; you may want their input.~_ ”

            Dr. Helvetica pushed a piece of paper with some names and phone numbers on it as well as a prescription stapled on the top left corner of the page.

            “I do appreciate everything, Dr. Helvetica, and I do hope you understand my decision,” Dr. Gaster said, reverting back to speaking in Common, taking the paper and standing.

            “It is always a pleasure, Aster. I know I haven’t been your pediatrician for long, but I hope I have served you both well and I do hope to continue to do so. This is just a very, very unfortunate turn of events.”

            “It is, and you have been wonderful to us, just this is too…”

            Dr. Gaster trailed off as she looked down at her daughter, who was still clutching the dolly and looking up at her. Sans was intelligent, and it was bad enough that she was going to know that something was wrong without her mother coming out and saying so.

            “Please let me know your decisions and keep me in the loop; I want to do everything I can to help,” Dr. Helvetica said, then he looked down at the child with a smile. “Also, Sans can keep the dolly.”

            “I will let you know what I find, Doctor, I promise, and thank you.”

 

~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~

 

            “Is that why I only have seen you and Papyrus?” Frisk asked. “Are you two the last of your kind?”

            Sans shrugged. “It’s hard for me to say for certain. All I do know is that I have never come across another skeleton besides my sis.”

            They continued to walk through Snowdin Forrest, Frisk realizing with some nostalgia that this was where they and Sans had first met as they walked through the gate that Papyrus had set up to stop any humans from entering the town. Sans must have taken notice, too, as she huffed a small bit of laughter as she glanced over her shoulder at the wooden structure.

            “I can’t believe she thought that thing would do any good,” Sans murmured.

            “So, what happened next? Did your mom take you to all of those doctors?”

            Sans nodded. “From what I can recall, she did,” a small sigh. “She did.”

 

~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~ * ~

 

            It had been about six weeks since they had seen Dr. Helvetica.

            Dr. Gaster sighed, her head in her hands as she looked over the papers spread before her. They all basically said the same thing, and no one wanted their child to be given a death sentence. She picked up the small box sitting beside her with a sigh, her eyes glancing over the words on the package. As many times as she saw words, she nearly had them memorized, but it didn’t matter; she read them again all the same.

            “Sans,” she called unenthusiastically, opening the box carefully, pulling out a small hypodermic needle and a glass bottle with blue liquid inside that glowed softly.

            In the time it took for her little toddler to come running to her, Dr. Gaster had filled the needle and placed it on the table, hoping her daughter wouldn’t see it.

            “Mommy?” Sans said, tilting her head to the side.

            Dr. Gaster smiled and picked her child up, setting her on her lap and hugging her tight with one arm while her other hand grabbed the needle.

            “Sorry, baby bones, just be good for me,” she murmured.

            Sans gripped her tightly, knowing full well what was coming, and letting out a wail when the needle was stuck into the back of her shoulder. Once the syringe was empty, Dr. Gaster rubbed the spot and kissed her daughter on the temple.

            “I’m so, so sorry, baby bones. Thank you for being such a brave girl.”

            Sans let out a small sob, rubbing her face in her mother’s lab coat. “Why, Mommy?” she said in a tiny voice.

            “Because it’s good for you, sweetheart, otherwise you’re going to become very, very sick,” she wrapped both arms around Sans, hugging her. “But I am so proud of you, my sweet, brave, baby bones.”

            Sans sniffled. “Can I go play?”

            “Of course, my love.”

            She set Sans back down, tickling her side a bit so she would giggle as she ran off. Dr. Gaster smiled at her daughter before putting the medicine away and turning back to the papers. She didn’t see the point anymore in shuffling through and reading them yet again, so she reached over for her phone and called Dr. Helvetica.

            “I’m very sorry, Dr. Gaster, but Dr. Helvetica isn’t in,” said the nurse on the other side of the line.

            “Do you know when he will be in?” she asked.

            “Uhm, well, I, uh, I’m so terribly sorry, Dr. Gaster,” the nurse said shakily and Dr. Gaster felt her insides run cold. “But Dr. Helvetica likely won’t be returning. He is very, very ill.”

**Author's Note:**

> Like what you read? over 18? Fontcest your jam? Then come visit me on my tumblr where I have stories not posted here on Ao3, I reblog interesting art work and other fics, and a whole bunch of neat stuff!  
> [SoloShikigami's Tumblr](https://soloshikigami.tumblr.com/)


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